Amplitude-Shifted-Keyed (ASK) modulation is useful for a variety of applications such as Amplitude-Modulation (AM) radio and more recently for Near-Field Communication (NFC). NFC devices are often very low power devices and may run on batteries or use inductive power coupling. The ASK transmitter may be the most power-hungry block in a NFC device. Thus highly power-efficient ASK transmitters are desirable for NFC and other applications.
NFC devices may have a highly efficient antenna that is formed by a spiral of printed metal traces that are formed on a printed-circuit board (PCB). These spiral inductor antennas have very low losses and have a high Q factor. The small antenna losses increase the fall time of the ASK envelope since energy leaks out of the low-loss antenna at a very slow rate. The amplitude stays high for a longer period of time, extending the fall time.
The slow fall time hinders high data rates. A more rapid fall time is desired to support higher data rates.
What is desired is a ASK transmitter with small power losses, yet has fast fall times. A highly power-efficient ASK transmitter with enhanced fall times is desired to achieve faster data rates.